BTO Research Report No. 483 An assessment of the feasibility of annual monitoring of winter gull roosts in the UK and possible outputs from such a scheme Authors N.H.K. Burton, I.M.D. Maclean & G.E. Austin Report of work carried out by The British Trust for Ornithology under contract to Natural England November 2007 British Trust for Ornithology British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU Registered Charity No. 216652 CONTENTS Page No. List of Tables...........................................................................................................................................3 List of Figures .........................................................................................................................................5 EXECUTIVE SUMMARY....................................................................................................................7 1. INTRODUCTION...................................................................................................................9 2. METHODS............................................................................................................................11 2.1 Identification of Sites Where Gull Numbers Surpass 1% Thresholds or Exceed 20,000 Birds ...........................................................................................................................11 2.2 Comparison of Species’ Indices Produced Using Wings and Webs Core Counts and Their Representativeness..............................................................................................12 2.3 Frequency of Existing Volunteer Counting of Gull Roosts and Interest Among Counters in Submitting More Regular Gull Roost Count Data..........................12 3. RESULTS ..............................................................................................................................15 3.1 Identification of Sites Where Gull Numbers Surpass 1% Thresholds or Exceed 20,000 Birds ...........................................................................................................................15 3.2 Comparison of Species’ Indices Produced Using Wings and Webs Core Counts and Their Representativeness..............................................................................................15 3.3 Frequency of Existing Volunteer Counting of Gull Roosts and Interest Among Counters in Submitting More Regular Gull Roost Count Data..........................16 3.3.1 Frequency of WinGS counts per winter.....................................................................16 3.3.2 Frequency of gull counting according to bird reports................................................16 3.3.3 Questionnaire responses.............................................................................................16 4. DISCUSSION ........................................................................................................................17 4.1 Identification of Sites Where Gull Numbers Surpass 1% Thresholds or Exceed 20,000 Birds ...........................................................................................................................17 4.2 Comparison of Species’ Indices Produced Using Wings and Webs Core Counts and Their Representativeness..............................................................................................18 4.3 Frequency of Existing Volunteer Counting of Gull Roosts and Interest Among Counters in Submitting More Regular Gull Roost Count Data..........................19 5. CONCLUSIONS AND RECOMMENDATIONS..............................................................21 5.1 Worth of Annual Monitoring of Gull Roosts......................................................................21 5.1.1 Identification of important sites .................................................................................21 5.1.2 Indexing of gull populations ......................................................................................21 5.2 Recommendations and Requirements for Implementing a System for Volunteers to Submit Gull Roost Counts and Future Reporting.........................................................22 Acknowledgements...............................................................................................................................24 References .............................................................................................................................................25 BTO Research Report No. 483 1 November 2007 Page No. Tables.....................................................................................................................................................27 Figures...................................................................................................................................................43 BTO Research Report No. 483 2 November 2007 List of Tables Page No. Table 3.1.1 Counts of Black-headed Gull in the UK exceeding national or international (winter) thresholds........................................................................................................27 Table 3.1.2 Counts of Common Gull in the UK exceeding national or international (winter) thresholds........................................................................................................29 Table 3.1.3 Counts of Lesser Black-backed Gull in the UK exceeding national or international (winter) thresholds........................................................................................................31 Table 3.1.4 Counts of Herring Gull in the UK exceeding national or international (winter) thresholds......................................................................................................................33 Table 3.1.5 Counts of Great Black-backed Gull in the UK exceeding national or international (winter) thresholds........................................................................................................34 Table 3.1.6 Numbers of sites surpassing national or international 1% thresholds for gull species using WinGS count data or WeBS annual report / core count data, and numbers of additional sites that surpass thresholds according to single counts noted in bird reports...........................................................................................................................36 Table 3.1.7 Sites which hold at least 20,000 gulls either according to WinGS counts or WeBS core count five-year peak means ..................................................................................37 Table 3.2.1 Numbers of gulls informing species’ indices for regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.................................39 Table 3.3.1 Frequency of gull roost counts at those WinGS key sites where counts of individual species exceeded national or international (winter) thresholds or which held at least 20,000 gulls, as indicated by data from WinGS, bird reports and questionnaires........40 BTO Research Report No. 483 3 November 2007 BTO Research Report No. 483 4 November 2007 List of Figures Page No. Figures 3.2.1 Indices for the numbers of Black Headed Gull wintering in regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.........................................................................................................................44 Figures 3.2.2 Indices for the numbers of Common Gull wintering in regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.........................................................................................................................46 Figures 3.2.3 Indices for the numbers of Lesser Black-backed Gull wintering in regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.........................................................................................................................48 Figures 3.2.4 Indices for the numbers of Herring Gull wintering in regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.........................................................................................................................50 Figures 3.2.5 Indices for the numbers of Great Black-backed Gull wintering in regions of Great Britain produced using a. WinGS counts from January 1953 to January 2004 (after Banks et al. submitted) and b. WeBS Core Counts from 1993/94 to 2005/06.........................................................................................................................52 Figure 3.3.1.1 The frequency that WinGS key sites (whole sites or, if divided, sub-sites of these) were surveyed for roosting gulls during winter 2003/04..............................................54 BTO Research Report No. 483 5 November 2007 BTO Research Report No. 483 6 November 2007 EXECUTIVE SUMMARY 1. The recent 2003/04-2005/06 Winter Gull Roost Survey (WinGS) estimated that the UK supported over 3.75 million gulls in winter. As in previous surveys, estimates were produced using counts of gulls